Postgraduate research opportunities

Additive Manufacturing of Ti alloys for medical implant applications

The objective of this PhD is to apply and compare two different AM methods of the laser metal deposition process and the selective liquid melting to produce an optimal biocompatible surface.

Number of places

1

Funding

Home fee, Stipend

Opens

9 July 2019

Deadline

1 October 2019

Duration

3 years

Eligibility

Applications are welcome from all UK, International and EU applicants.

Applicants must have, or expect to get, a 1st or good 2:1 degree (or Masters with Merit) in a relevant subject

Project Details

Rectifying large bone defects through surgery poses a number of challenges. With varying geometries these defects are typically strengthened or replaced with a range of materials including titanium in its pure or alloyed form. Titanium offers a number of advantages including biocompatibility, high resistance to wear and corrosion as well as high strength and a promotor for osseointegration. However, a major disadvantage if that the titanium, which comes in a stock form of plates, needs to be manually manipulated during surgery to fit the required shape. Apart from being a time-consuming and cumbersome process the bent plates may have a proposition to fatigue fractures due to the stresses induced by the bending.

Additive manufacturing provides an alternative to this so-called traditional approach offering, through techniques such as laser metal deposition (LMD), selective laser melting (SLM) and electron beam melting, the ability to provide customised reconstruction plates based on accurate 3-D measurements of the patient.

 

The challenge:

In comparison to conventionally manufactured parts, AM generates a relatively rougher surface which typically requires further post-processing such as finish machining or polishing. Post-processing also serves a secondary purpose of eliminating surface flaws and defects reducing the likelihood of crack initiation and propagation. Both the surface finish and macrostructure have a significant impact of the performance of the implant.

Conversely, a smooth surface may not be that beneficial from a biological standpoint as factors such as surface chemistry, surface potential, roughness and the hydrophilicity all have an influence of the adhesion, cultivation and growth of cells and bacteria on the implant. The ultimate success of an implant i.e. acceptance by the body and integration are very much dependent on the adhesion of proteins and the formation of a biofilm on the implant surface. From a functional perspective if the surface is too rough then this may influence the tribological performance of the implant resulting in accelerated wear and a reduced service life. For all these reasons, several treatments have been suggested and applied with the aim of modifying surface characteristics to improve both surface chemical composition and roughness.  Treatments can be divided into three main categories:

(i) Physical (e.g. cutting and turning, blasting, smoothing and etc.)

(ii) Chemical-electrochemical (i.e. immersion of metallic samples into polar solution (organic or aqueous), Deposition methods)

(iii) Biochemical method (Adsorption: immersion of the metallic sample into a bioactive peptide containing solution. Covalent attachment: covalently bind the bioactive peptide, either directly or through a spacer.)

 

Funding Details

Funding provided will cover Home Fees and Stipend.  International students must provide evidence of their ability to pay the difference in fees between Home and International.

Further information

Objectives:

The objective of this PhD is to apply and compare two different AM methods of the laser metal deposition process and the selective liquid melting to produce an optimal biocompatible surface.

Laser metal deposition offers a number of advantages over other AM techniques including rapid surface build-up, the ability to deposit different materials on a substrate and greater flexibility in part complexity.  On the other hand, selective liquid melting offers a better mechanical performance which is due to the higher density of manufactured parts by this technique.

 

Our strategy:

The strategy for the first part of this work will be: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish. A number of LMD process parameters will be investigated along with the powder properties and flow rate which all influence the surface quality, thermal history, residual stress as well as metallurgical and mechanical properties of the generated part. Our partner in UofW is developing a model to simulate residual stresses and surface roughness during selective laser melting. The model and the expertise and the experimental work accomplished at UofW will be leveraged to help us in optimizing the process parameters in order to achieve a minimum residual stress and surface porosity reducing the need for post-processing operations.

Surface analysis

The manufactured parts will be characterised at Strathclyde for metallographic and topographic properties before undergoing any further surface treatment. After the final mechanical surface treatment, the biological treatments which aimed at controlling/ guiding the complex sequence of biochemical phenomena that take place at the interface between implanted devices and biological tissues will be performed. This part of the project will be done in collaboration with TriPhyll Inc. TriPhyll is a Canadian company active in antimicrobial and Anti-aggregation Coating Technologies.

 

 

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